A mineral bearing geological formation may include many different layers from which commercially valuable products may be obtained. In some instances, it may be desirable to recover gases from a substantially porous layered medium. That layered medium may or may not have been a zone from which commercial recovery of a product was originally foreseen at the time of original exploitation of that geological formation. However, the overall commercial recovery from well drilling and production operations may include an opportunity to obtain value by enhancing recovery from other layers of the formation.
In some instances, that opportunity may relate to the recovery of a commercially valuable fluid, such as a hydrocarbon gas. The gas may initially be stored by sorption on the large surface area of the grains of a porous substrate, such as, for example, coal grains. Commercial extraction may commence if the reservoir pressure is lower than the desorption pressure. Secondary porosity in the porous matrix may tend to provide a flow pathway for production. For example, in the context of coal, the secondary porosity features may be referred to as cleats or macropores which represents the macroporosity of the coal. It may be advantageous to encourage or stimulate gas production from such a porous matrix by, for example, increasing the size, number or network density connectivity/intersections of the cleats and macropores.